You probably gave it a wrong "name", which is the first field in the "File" properties tap of the Plone CMS on pure-data.org|iem.at The "name" must be a valid filename including all suffixes, otherwise downloaders run into this problem.
oh I see. it's weird because my browser downloaded it as uPDated.gz anyway I've renamed it: http://pure-data.iem.at/Members/gerard/uPDated.dmg.gz
thanks
... gerard